Process of making tungsten carbide product



Oct. 20, 1936. O s 2,057,786

PROCESS OF MAKING TUNGSTEN CARBIDE PRODUCT Filed May 26, 1930 I? van for 'O-scar Z. Nil/s Afforn ey Patented 20, 1931i 'PATENTQOFFICE PROCESS OF CARBIDE MAKING TUNGS'I'EN raonuc'r Oscar 1.. Mills, Los Angeles, Calif., assignor to Mills Alloys Inc., Los Angeles, Call! a corporation of Delaware Application May as, 1930, Serial No. 455,132

-6Ciaims.

This invention relates to a process of making a product that is capable of withstanding heavy wear without breaking or chipping, as for example, a cutting tool such as are used for turning and boring metal parts.

Tungsten carbide is now a well-known product,

and can be commercially manufactured by the aid of an electric arc furnace of the character described in my Patent Number 1,719,558, issued July 2, 1929. For some purposes, such as-for cutting tools, the grain structure of the tungsten carbide must be tough and free from internal stresses so as to withstand the strains imposed upon the tool without cracking, thereby maintaining a proper cutting edge, which yet retains a very high degree of hardness. Thus even manganese steel can be readily machined.

It is one of the objects of my invention to make it possible to produce this extremely durable material in commercial quantities and inexpensively, and particularly by casting the article to be formed directly in complete form.

Although I prefer to utilize tungsten carbide without any other element, a small percentage of free carbon or of other material such as boron, silicon, cobalt, nickel or chromium may be employed, but only to a sparing extent. Such alloying materials, which of course tend to reduce the hardness very materially, are not essential in my process, because I secure the desired good grain structure due to my improved treatment of the material.

My process produces a product that has obviously great advantages. It can be used to machine iron or steel or other materials, either metallic or non-metallic, at amuch greater speed than by any of the common forms of tool steel or metals. These advantages I believe are due to steps in the process that first insure a noncrystalline, fine grain structure of substantially pure tungsten carbide; and that next prevent shrink strains. These steps will be described in detail in the specification.

My invention possesses many other advantages, and has other objects which may be made more easily apparent from a consideration of an embodiment of my invention. For this purpose I have shown a form in the drawing accompanying and. forming part of the present specification. I shall now proceed to describe this form in detail, which illustrates the general principles of my invention; but it is to be understood that this detailed description is not to be taken in a limiting sense, since the scope of my invention isbest defined by the appended claims.

Referring to the drawing:

Figure 1 is a diagrammatic side elevation of an apparatus useful in making my novel product;

Figure 2 is an end view thereof, one of the parts being shown in section;

Figure 3 is a detail sectional view of a mold used in my process;

Figure 4 is a top view of a form which my product may take after casting; and

Figures 5 and 6 are respectively top and side views of a cutting tool fashioned by the aid of my process.

In practicing my process, I first produce a molten tungsten carbide mass, at a temperature above its melting point; for example, by the aid of the inventions disclosed in my prior Patents 1,719,558, issued July 2, 1929, and 1,721,966, issued July 23, 1929. This mass preferably has by weight, not less than 2' percent of carbon, nor more than 6 percent thereof. It can be alloyed with other metals, but preferably there should not be more than 8 percent by weight, of such materials or other impurities. Among such alloying metals may be mentioned the iron group, chromium, molybdenum, tantalum, boron, silicon, thorium and titanium.

When the mixture is thoroughly and completely molten, as in a carbon crucible capable of accommodating at least several pounds of the material, its temperature of course is tremendously high; somewhere in the neighborhood of 5000 to 6000 degrees Fahrenheit. It is then poured into a mold of the desired configuration, and subjected to pressure for the purpose of securing a fine grain structure.

I prefer to cast the molten material in a mold that does not form a gas, but that is capable of absorbing and transferring the heat of the product. Refractory molds made from carbon or graphite are not suitable, because they have a tendency to 'impart porosity to the product; and accordingly I prefer a copper mold or the like, which cannot react with the molten mass, and which is capable, I have found, of withstanding the heat, mainly because it rapidly transmits the heat away.

I have indicated in the present instance, a mold structure that is capable of casting a product such as a ring ll (Figs. 3 and 4) of about 10 inches outside diameter, one inch wide and about three-eighths of an inch thick. However, other forms or sizes could be used.

While the material is still molten, it is subjected to pressure, as above mentioned. A convenient way of accomplishing this is by the aid of centrifugal force. Thus the mold structure can be so arranged that it can be rotated to throw the molten material against a circular wall to form the ring II.

The mold structure itself, as shown most clearly in Figs. 1, 2, and 3, can include a lower section I? of copper or equivalent material, and an upper section I3 01 the same material. These two sections, when superimposed, define a space I having a contour into which the product II is to be cast; in the present instance, space I4 is formed by shallow depressions in the contiguous faces of the mold sections l2, l3. These sections can be hinged together, as at M. Ring II is shown inside mold ll-l2 in Fig. 3. Upper section l3 can have a large central aperture l5 to permit pouring the molten tungsten carbide into the closed mold, which is rotated about a vertical, central axis, in order to throw the material into the position indicated. The pressure thus -attained may be of the order of or 100 pounds per square inch. Although higher or lower values could be used.

To provide this rotation, I show in this instance a shaft I 6 joined to the bottom of mold section l2, that can be rotated by any source of motion. For example, in Figs. 1 and 2, I show shaft it supported in a bracket structure I! on a table [8, and a small electric motor l9 also conveniently supported on the table, drives the shaft l6 through gearing 20.

As soon as the product ll assumes a form that is self-supporting, and while it is still white hot, and not entirely solid throughout, it is immediately ejected into a space where it is gradually cooled. The copper mold of course serves to produce by cooling an overlying layer of solid carbide for the article ll, even if its interior is still fluid. A space for gradually cooling it to room temperature can be formed by a box 2| that contains some powdered material that retains heat long enough to insure slow cooling. For

, example, a mass of silica. flour 22 can be used in the box 2|, which is preheated to about 500 Fahrenheit, as by an electric heating element 23. The sides and bottom of the container can be provided with a layer of heat insulation.

To facilitate immediate ejectment of product I I into container 2|, table l8 can be collapsed, as by folding legs 24 out from under the table, whereupon the table, being hinged at 25 on support 26, tilts downwardly and drops the product ll out of the mold l2-l3, which also opens bythis dropping movement. Of course other means for immediate ejectment into a slow cooling space could be used. This slow cooling effectively prevents internal strains due to shrinkage.

After cooling to about room temperature, the product II is placed in an annealing furnace, and heated to a temperature of about 3600 Fahrenheit. It is then allowed to cool slowly.

This annealing assists in producing a homogeneous, silky structure free from crystals and sufliciently hard and tough to wear for a long period.

Product H can directly take the form of any desired finished product: but in the present instance, I indicate that the ring can be broken into a number of short pieces, and be used as cutting tools, such as 21 (Figs. 5 and 6). The cutting edge 28 can if desired be subsequently ground to'produc'e a conventional cutting tip, but this is not essential, for the natural fracture can be utilized in most instances for this purpose.

I claim:

1. The process which comprises pouring molten tungsten carbide at a temperature above its melting point into a mold chemically inert to tungsten carbide, subjecting said material to pressure without the addition of heat thereto, until it assumes a state sufliciently cool to be self-supporting, and then ejecting said material into a place where it can cool slowly.

2. The process which comprises pouring molten tungsten carbide at a temperature above its melting point into a mold chemically inert to tungsten carbide, subjecting said material to pressure without the addition of heat thereto until it assumes a state sufliciently cool to be self-supporting, and cooling saidmaterial slowly by contacting it with material having slow heat transferring properties.

3. The process which comprises pouring molten tungsten carbide at a temperature above its melting point into a mold, subjecting said material to pressure until it assumes a state sufliciently cool to be self-supporting but not completely solidifled, ejecting said material into a place whre it can cool slowly, and subsequently raising the temperature of the product to a degree sufficient to anneal it, but below its melting point, and slowly cooling it from that temperature.

4. The process which comprises pouring molten tungsten carbide at a temperature. above its melting point into a cool mold that is chemically inert as regards the carbide, subjecting said material to pressure until it assumes a state sumciently cool to be self-supporting, cooling said material slowly by contacting it with material ,having slow heat transferring properties, and subsequently raising the temperature of the product to a degree sufficient to anneal it, but below" its melting point, and slowly cooling it from that temperature.

5. The process which comprises producing entirely molten tungsten carbide, casting said carbide while molten under pressure without the addition of heat thereto, and excluding further absorption of carbon during casting, solidifying said casting by slow cooling to room temperature for preventing shrink strains, and annealing the casting.

6. The process which comprises pouring molten tungsten carbide at a temperature above its melting point into a chemically inert mold, subjecting said material to pressure without the addition of heat thereto, until it assumes a state sufficiently cool to be self-supporting, removing said material from the mold and placing it where it can cool gradually.

OSCAR L. MILLS. 

